#include <fstream>
#include <iostream>

using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");

int val( int& st , int& dr , int a[5000000])
{
    int i,minn = 10000000;
    for(i = st;i<= dr;i++)
    {
        if(a[i]<minn)
            minn = a[i];
    }
    return minn;
}

int main()
{
    int n,m,i ,minn = 10000000 ;
    long long sum=0;
    fin>>n>>m;
    int a[n] ,st,dr;
    for(i=1;i<=m;i++)
    {
        fin>>a[i];
        if(a[i]<minn)
            minn = a[i];
    }
    st = 2;
    dr = m+1;
    sum += minn;
    //cout<<minn<<" ";
    for(i=m+1;i<=n;i++)
    {
        fin>>a[i];
        if(a[i]<minn)
        {
            minn = a[i];
        }
        else
        {
            if(minn == a[st-1])
                minn = val(st,dr,a);

        }
        sum += minn;
        //cout<<minn<<" ";
        //cout<<minn<<" ";
        st++;
        dr++;

    }
    fout<<sum;
    return 0;
}